Field of the Invention
The present invention relates to a catalytic converter with electric heating, including a housing containing at least one honeycomb body configuration through which an exhaust gas of an internal combustion engine can flow in a flow direction, the honeycomb body configuration being electrically conductive at least in partial regions, being heatable and having a catalytically active coating at least in partial regions.
Electrically heated catalytic converters are described, for instance, in U.S. Pat. No. 5,146,743. A more sophisticated construction, which is the point of departure for the present invention, is described in International Patent Application WO 92/02714, corresponding to U.S. Pat. No. 5,411,711. It is also known to heat the honeycomb bodies that are used in electrically heatable catalytic converters, nonhomogenously. To that end, International Patent Application WO 92/13635, corresponding partially to U.S. application Ser. No. 08/353,964, filed Dec. 12, 1994, proposes perforating metal foils used in the honeycomb body with slits or holes, in order to influence a current distribution.
The known structures for electrically heatable honeycomb bodies, while fundamentally suitable for most applications, nevertheless make it difficult, for various given peripheral conditions, to create standardized models that are mechanically stable and at the same time meet the electrical and thermodynamic demands made of them.
It has been found that electrically heatable catalytic converters have to be adapted to virtually each vehicle type, if optimal results are to be attained. In order to do so, first a maximum current intensity available for heating must be taken into account, and an electrical resistance of the honeycomb body, at a given supply voltage (usually 8 to 12 V) must orient itself thereto. Since an electrically heatable honeycomb body should be disposed as close as possible to and upstream of a following non-heatable catalytic converter, such as a precatalyst or a main catalyst, the diameter of the electrically heatable honeycomb body must be adapted to those given situations. Moreover, the available heating area in proportion to the heated mass is important, which makes it desirable to be able to vary that proportion over a wide range. It is precisely that which is quite difficult in the known models having a fixed resistance and a fixed diameter. In particular, certain peripheral conditions would require quite axially short heatable honeycomb bodies, which are not sufficiently stable mechanically and above all cannot withstand the vibrations that occur in motor vehicles.